The present invention relates to a method of packing articles and of the kind whereby a number of strips of packing material is conducted through a station wherein a cross section shape is applied to each strip in such a way that the strips may accommodate the articles to be packed, through a filling station at which articles are arranged into the strips, through a longitudinally extending welding station at which the longitudinally extending margins of each strip of material are welded together in order to form packing tubes, through a cross welding station comprising a set of heating welding means for heating the packing tubes between the articles and comprising a set of clamping welding means for clamping the heated parts of the packing tubes, and through a separation station comprising transverse cutting means and securing means and wherein a reciprocating stroke movement is applied to the sets of welding means belonging to the cross welding station, and said sets of welding means are moved for engaging and disengaging the strips of material.
By means of a known method of the kind referred to above, a stroke movement is used, the stroke length of which corresponds to the length of the packings to be produced, and the set of heating means and the set of clamping means are arranged with a mutual distance which corresponds to the length of the packings, and the two sets of welding means are moved for engaging the strips of material and moving the strips during the forward stroke movement, and during this stroke movement, the heating means heat the strips of material, caught by the heating means between the articles positioned in the strips of material and simultaneously the clamping means clamp the parts of the strips of material which were heated by the heating means during the preceding stroke movement. When the stroke movement has been completed, the sets of heating and clamping means are disengaged from the strips of material, and said sets of welding means are moved back to their starting position. During the return movement, the strips of material are secured by means of a combined cutting and securing device in such a way that the strips of material are not moved backwards together with the disengaged sets of welding means. When the sets of welding means have returned to their starting position, they are again moved for engaging the strips of material whereby the heating means will heat new parts of the strips and the clamping means will clamp the parts of the strips heated during the preceding stroke and will cool said parts in such a way that transverse seals are obtained.
As regards the prior art reference should be made to Danish Pat. No. 104,287 which, however, mentions one strip of material only, but later on the prior art known from said specification has been used in connection with packing machines adapted to more strips.
According to the known method, no difficulties exist as regards maintaining the areas of the packing tubes, at which the tubes are to be welded, free from articles. It is only necessary to position the articles in the strips of material at intervals which are longer than the areas to be welded and to locate such intervals at a definite distance from the reversing points of the stroke movement. However, it is difficult to provide for a synchronization of the strips of material with respect to the articles, in the following termed registration, in such a way that the articles always will be positioned at predetermined parts of the strips of material so that the cross weldings may be positioned at predetermined positions of the strips of material. Accordingly, strips of material have previously been used which are patterned in such a way that one pattern is repeated at comparatively short intervals, whereby it is achieved that it will be rather inconspicuous if a cross welding is positioned within a pattern. On the contrary, it is not possible to use strips, the patterns of which have a length of pattern corresponding to the length of the packing requested, because it previously has not been possible to secure that the cross weldings will be positioned exactly at the transitions between the patterns. This is due to the fact that, first of all, an uncertainty exists as regards the printing of the patterns upon the strips because an exact predetermined pitch of pattern cannot be secured. Moreover, during the cross welding, which comprises first a heating and then a clamping operation, a non-defined change of length of the strips of material occurs, and accordingly it is not sure that one and the same length of strip will be supplied to the apparatus during each of the strokes of the packing apparatus. Accordingly, it may easily happen that great errors of registration may occur, due to accumulations of small errors of registration, and accordingly the risk exists that a welding will be made between the ends of a pattern, even though it is requested to position the weldings between the patterns.
It is an object of the present invention to provide a method of the kind referred to above by means of which it is very simple to achieve a correct registration in such a way that identical pieces of strips of material form each final packing, and wherein each such piece of strip comprises a complete pattern or a multiple of complete patterns.